This is my model: I measured the chair and made a single rectangle of the length of the back + the length of the seat. I rounded the upper part of the backrest. I applied to the wrong side of the zone of separation between the seat and back a strip of stretch to keep separated and block movements of the two fillers and finally I applied the invisible zip on the exposed part. In this way, if I have to wash the pillow just to open the zipper and then stretch to remove the padding. (I hope I was clear and I'm sorry for the bad English!)